1. Field of the Invention
The present invention relates to a suction and discharge valve mechanism for a fluid displacement apparatus. More particularly, it relates to a configuration of a suction and discharge valve mechanism for a reciprocating piston-type refrigerant compressor used in an automotive air conditioning system.
2. Description of the Related Art
Piston-type compressors, such as swash plate-type compressors and wobble-type compressors, are known in the art. For example, U.S. Pat. No. 4,776,259 to Takai describes an air conditioning device used for a vehicle employing a multi-cylinder, piston-type compressor with reciprocating pistons and a suction and discharge valve mechanism.
In the following description, the right side of each figure is referred to as a rear or rearward end, and the left side of each figure is referred to as a front or forward end. With reference to FIGS. 1 and 2, a wobble plate-type compressor is shown comprising a compressor housing 11 having a cylinder block 11b fixed at a rear end of compressor housing 11, and a front end plate 10 disposed on a front end opening of compressor housing 11. A cylinder head 18, defining a discharge chamber 20 and a suction chamber 19, is mounted on the rear end opening of compressor housing 11 behind a valve plate 18a.
A discharge valve assembly is mounted on a rear end surface of valve plate 18a. Valve plate 1 8a has a discharge hole 20a extending therethrough to allow communication between the compression chamber and discharge chamber 20. The discharge valve assembly comprises a discharge valve 22 and a valve retainer 21, which is secured to a rear end surface of valve plate 18a by bolt 23.
Referring to FIG. 2, valve retainer 21 limits the bending movement of discharge reed valve 22 in the direction in which the refrigerant gas exits a cylindrical bore 17 and enters discharge chamber 20 through discharge hole 20a. Discharge reed valve 22 has a modulus of elasticity which keeps discharge hole 20a closed until the pressure in cylindrical bore 17 reaches a predetermined value.
Compressor housing 11 defines a crank chamber 13 that is adjacent to cylinder block 11b. Cylinder block 11b is provided with a plurality of equi-angularly spaced cylindrical bores 17. A drive shaft 12 is rotatably supported at its rear end by cylinder block 11b through a bearing 12b, and at its front end by a front end plate 10 through a bearing 12a. A cam rotor 14 is fixedly mounted on drive shaft 12 by a pin (not shown) and rotatably supported relative to a rear end surface of front end plate 10 through a thrust bearing 12c. A wobble plate 15 is disposed on a reduced diameter portion 15b of cam rotor 14 that extends axially outward from the inclined cam surface of cam rotor 14. A thrust bearing 14a is interposed between wobble plate 15 and the inclined cam surface of cam rotor 14.
Wobble plate 15 is prevented from axial movement on reduced diameter portion 15b by restraining ring 15c. A reciprocating piston 16 is received in each of cylindrical bores 17. Each piston 16 is connected to wobble plate 15 through a piston rod 16a. A restraining means 15a comprises a slot formed in the peripheral surface of wobble plate 15 and slide plate 11 a mounted in the bottom portion of crank chamber 13 and extending axially thereof.
Discharge reed valve 22 strikes a rear end surface of valve plate 18a when it closes. This striking generates vibration and noise during the operation of the compressor. Vibration, caused by discharge reed valve 22 striking a rear end surface of valve plate 18a, is readily transmitted to compressor housing 11.
One proposed solution to overcome the above-mentioned disadvantages is described in Japanese Unexamined Utility Model Publication No. H4-119,370. That application describes a compressor wherein a valve mechanism includes circular plate members connected to the drive shaft. The rotation of the drive shaft and the circular plate members opens and closes the suction conduits and the discharge conduits.
Another proposed solution to overcome the above-mentioned disadvantages is described in Japanese Unexamined Patent Publication No. H5-126,040. The application discloses a compressor wherein a valve mechanism comprises a rotary valve or a piston, or a rod, in lieu of circular plate members. The valve mechanism opens and closes the suction conduit and the discharge conduit, respectively.
However, in the configuration of the valve mechanism comprising circular plate members and a rotary valve, the sliding contact surfaces do not move smoothly with respect to each other, and the sealing performance between the sliding contact surfaces is decreased. As a result, an manufacturer is required to carefully control the clearance of the sliding contact surfaces in assembling the compressor. Thus, this configuration is difficult to manufacture and expensive to assemble.
Further, in the configuration of the compressor comprising a piston or a rod, the valve mechanism acts to either fully open or fully close a suction conduit and a discharge conduit during a suction stage or a discharge stage of the compressor. The valve mechanism does not permit opening a fraction of an area of the suction conduit and the discharge conduit, i.e., a suction conduit is fully opened and a discharge conduits is fully closed when the compressor moves from the suction stage to the discharge stage. Thus, the suction conduit and discharge conduit are opened fully and closed fully without considering the reciprocating speed of the piston.
Generally, a piston within a cylinder reciprocates with speed reaching zero at the bottom dead center and top dead center positions, and with maximum speed at a position halfway between bottom dead center and top dead center. Thus, it is difficult for a piston to reciprocate smoothly within a cylinder because the replacement fluid sucked into and discharged from the cylinder has an inertia force. This results in a decrease in the compression efficiency.